It is generally known that mechanically stabilized earth (MSE) is soil typically constructed with artificial reinforcing. It can be used for retaining walls, bridge abutments, dams, seawalls, and dikes, wherein reinforcing elements may vary, but generally include steel and geosynthetics to prevent erosion of soil. Although the basic principles of MSE have been used throughout history, MSE was developed in its current form in the 1960s.
Modern use of soil reinforcing for retaining wall construction was first pioneered by French architect and engineer Henri Vidal in the 1960s. The first MSE wall built in the United States was accomplished in 1971 on State Route 39 near Los Angeles. It is estimated that since 1997, many more than 23, 000 MSE walls have been constructed in the world.
As noted, the reinforcement materials of MSE can vary. Originally, long steel strips 50 to 120 mm (2 to 5 in) wide were used as reinforcement. These strips are sometimes ribbed, although not always, to provide added resistance. Sometimes steel grids or meshes are also used as reinforcement. Several types of geosynthetics can be used, including geogrids and geotextiles. The reinforcing geosynthetics can be made out of high density polyethylene, polyester, and polypropylene. These materials may also be ribbed and come in varying sizes and strengths. Generally, these geosynthetics are adhesively fastened to the backfill side of an MSE structure during construction, such as representatively depicted in FIGS. 8 and 9, wherein filter fabric strip F is shown, with adhesive glue G serving as fastener. As shown, bearing pad B even in combination with filter fabric strip F is unable to impede passage of fill through the joint, such that growth of undesirable vegetation V stems therefrom.
In other types of arrangements known in the art for reinforcement of MSE structures, rebar rods may be wrapped with the geotextile, wherein the rebar serves to structurally reinforce the MSE structure and the geotextile extension functions to limit movement of fill proximate the wall. Rebar rods positioned with in a MSE structural joint, however, inherently block the flow of water therethrough, disadvantageously enabling potentially damaging pressure build up.
By way of further background, and with reference to “Mechanically Stabilized Earth Wall Inspector's Handbook,” State of Florida, Department of Transportation, Sep. 14, 2000, the disclosure of which is herein incorporated by reference in its entirety, established procedures are in place for the construction of a MSE wall system. For example, during preparation of a site, soil reinforcement and select backfill must be prepared for the MSE wall footprint area, including the zone of the wall facing. The foundation for the structure must be graded level for a width equal to or exceeding the length of soil reinforcement, or as shown in the plans. Any soft or loose material that is encountered should be stabilized. The wall system may comprise original ground, concrete leveling pad, wall facing panels, coping, soil reinforcement, select backfill, and any loads and surcharges. All of these foregoing items have an effect on the performance of the MSE wall and are taken into account in the stability analysis. A change in any of these items could have a detrimental effect on the wall.
Once the area has been properly prepared, a concrete leveling pad is typically poured in place. Coping is used to tie in the top of the wall panels and to provide a pleasing finish to the wall top. It can be cast-in-place or prefabricated segments. As noted and as representatively shown in FIGS. 8 and 9, filter fabric is typically used to cover the joint between panels, and is typically placed on the backside of the panels. This keeps the soil from being eroded through the joints and allows any excess water to flow out.
Random backfill may be allowed in normal embankment construction. Select backfill meeting the gradation, corrosion, unit weight, internal friction angle and any other requirements of the MSE structure specifications will typically be used. Soil reinforcement will be used to hold the wall facing panels in position and to provide reinforcement for the soil. As noted above, the soil reinforcement can be strips, grids, or mesh. The reinforcement can be made of steel (inextensible materials) or polymers (extensible materials). Wall panel spacers, or bearing pads B, are used and are typically ribbed elastomeric or polymeric pads inserted between the panels. The panels or panels are used to hold the soil in position at the face of the wall, and are typically concrete but they can be metal, wood, block, mesh or other material.
The subject matter of the present disclosure is intended to enhance these well-established practices, relevant to known MSE wall structures, wherein exemplary MSE wall structures known in the art frequently show undesirable vegetation, such as depicted in FIGS. 8-10. MSE walls are typically constructed with an inch joint spacing between precast concrete panels, commonly 5′ square. The joints are typically covered with a strip of filter fabric F (+/−18″) glued G to a back fill side of the panel with adhesive during construction, such as depicted in FIGS. 8 and 9. The filter fabric F allows water to pass through the joints, and limits some movement of back fill therethrough; nevertheless, the known use and installation of filter fabric F is disadvantageous in view of the present disclosure.
That is, it is readily apparent that there is a need for improved drainage systems that may be either initially or retroactively installed, and that allow water to drain through MSE structure joints while also effectively preventing backfill from migrating through the joints, thus eliminating or dramatically reducing the unwanted vegetation.